Man United and Chelsea tracking Dortmund star

The German giants are worried one of their star assets will quit the club at the end of the season, with contract negotiations at a standstill.

Kagawa, who has a deal with Dortmund until 2013, has previously claimed moving to Manchester United would be a 'dream'. And with Sir Alex Ferguson eager to develop his squad in the summer, the Japanese international is on his radar.

The 23-year-old has scored 12 goals in 25 Bundesliga matches so far this season and his performances have alerted a string of top European clubs.

It is understood Kagawa favours a move to United but Chelsea are also keen, with a summer bidding war set to ensue.